Automatic rural crossbar switching system



J. DAVIDSON, JR

AUTOMATIC RURAL CROSSBAR SWITCHING SYSTEM April 3, 1956 Filed Jan. 16, 1953 5 Sheets-Sheet l I) van.

INVENTOR JOHN DA V/SO/V, di?. BY

ATTORNEY April 3', 1956 .1. DAVIDSON, JR 2,740,841

AUTOMATIC RURAL CROSSBAR SWITCHING SYSTEM Filed Jan. 16, 1953 5 Sheets-Sheet 2 ATTORNEY April 3, 1956 J. DAVIDSON, JR

AUTOMATIC RURAL CROSSBAR SWITCHING SYSTEM Filed Jan. 1e. 195s 5 Sheets-SheeI 5 @NNY l/OH/V DA V/050/V, L/R.

a/srmvr RURAL oFF/cf. F16. 4.

ATTORNEY April 3, 1956 J. DAVIDSON, JR 740,841

AUTOMATIC RURAL cRossBAR swITcHING SYSTEM April 3, 1956 J. DAVIDSON, JR

AUTOMATIC RURAL cRossBAR swITcHTNG SYSTEM 5 Sheets-Sheet 5 Filed Jan. 16, 1953 ATTORNEY lUnited States Patent Oce f 2,740,841 eiierrred Arr 3, 195.6

2,140,851 AUTOMATIC RU-RAL CROSSBAR lSWITC-HING :SYSTEM John Davidson, Jr., Upper- Montclair, N. I., assigner to 'International-Telephone and Telegraph Qgxpqmgon, a 'corporation of Maryland Applikation January 16s 51953,; Seralfle- 33,11 I1o claims. retira-azz) The rrevrrien of telephone Servire in sperren/settled rural sections has often necessitated the use of magneto telephones. and has required therertieee ef .rrdYidiLlSina f arrnershorne or storeto set up o.r 4taire dopvrrthe c =nreeieris- Although such arrangements. havehad 599s? rr'xznn nur u. 1... gnumg,

Fig. 2 shqws arural subscribers line circuit;

` 31shouis `a lcrossbar switching circuit, such as is pros ided aatltherural olices;

Fglfi lshort/s arural interoilce trunk circuit;

5 `Figj lshows arnaster office trunk circuit; and

atically illustrates tone` interruptor and cem't'rolV car`-eguiprnent provided at the rural o ces." I proposed'aiitomatic system, which is preferably limitedfto'small rural installations of approximately l0 l() line-s," 'provides practically the sante 4Oprating features aslare obtained with dial telephones but doesnot lneczess"ita't'e .fili-e buse vof dials .at vthe subscribers" stations. s Yis.lillusl'rajitec'l in Fig. l, the switching equipment is eullirabl'efer 'establishing' eerrrr'eerer's berweerrlruieeibers ii/ithiii any rural area 1 3, C, D .o1-1E, -between subscribers tiifofalcljacent rural areas, s uch as, for example, D, between subscribers in two ruralareas, separated by one or rnb're other rural areas,` such as, for f example, 'between subscribers vin ofliceB'and oiie, D, and between a rural subscrlbervand the master oice A, 'nher an operator handles more distant connections to and lrolrnihe rural area which involves additional charges. E alirural subscriberis provided with a crd'brfrniniature et/er, srch an .arrangement not 'conclusive t9 e996 'ifelebhene Service since difficulties are erperierreed in bfirrirs the ,erover type of people tskperfrrrr the Operaties stier fer'a eemmerrrlrete ,ealarvfand bessere the ,tretrrewbiehie .erisnafed 12v-these rural ee, isleatremelvlisht if isneeeeearyhhthe eqrrirA operating enpensesbe lcept to aminimur'n.

One object ofthe present l invention is Athe .provision ofnanwinexpensive rural crossbar telephone s ivithin'gsystem. v l 1 ich. v.'i ll permit magneto subscribers tStabliSh local calls without theaidot an operator ,andlxvitholt' changes in their existing magneto station equiprnent. Toll c alls l,which require detailed information Ato tirne'of conversation are established A'through a master ,o iffiewith theaidofan operator.

According tonne featureof my invention coniniutator means is provided at a central Aofiiceor .positiom which, responsive to an operation at acallingstation, cyclically prepares the central oice switching equipment successively to make ,connection to vthe station.lines in turn, successivelyand in synchronism transmits to the c ng'statiOnline distinctive Isignals.characteristie of the yidentity of thesta t io n` lines to which connections `"are cylicallyprepared Responsive to aiurther tirn'ed operat thefealling station the switching equipment at the .eerirraldee ie .serrated le eemnlete .la-Prepared e013- nection to ,a wanted station line.

'Accordingto a further feature of rny inventiondhe switching equipment at the central oice' conpr ises"a crossbar switch, the stationlines Aand trunks b eingcon- `nested lwothto horizontal and vertical terminals thereof. ,Me-ans is provided at the centraloice, which, responsive to a calling `signal sent frorrna calling station, causes the nergigation of a horijLontal magnet partieularthereio and vcy :li c all`f prepares circuits for the Vertical on holding in agnets and causes. the Attlrismission over theealling line v of audible signals characteristic of ,the 5identity ofltlie connections as they. are prepared. A'transmission of a. f ur.t her,signal from thecalling station, a circuit-.js .completed for the appropriate vertical magnet. ,togestab- Al ish,the connection to a wanted st ationnlineortrunk.

`-These and other features of the .invention vwill abe .described more fully in thefollowing detailed specification. Inthe drawings whichaccompany thetspecification, Eig. `1. illustratesthexlayout o'f a rural, area. comprising Y-fcnlr..rural. odices B,C, D anckE, anda masteroieA;

fiice wrth another subscriber in .thez same arearhe lreniove receiver from the A sfu/itch hook, the ,syl/itching equipment `autl'Alis'fen` tolthe tonecode'fs'igna'ls representing@thesubscriberswhoean be reached ,v 'vithout going another rural oiice. Wheniliefcalling subscriber learisthe ycode signal of the desired party,flv1e a5 will ytsraregrssswach hooker, depress if'f'o'r an insfanffif ,the ruralulinesare arranged -for .condition battery operation. .'lhe crossbar switching equipment then .functions vto Aes blish the connection. The calling slib-S-eriiberv will l lriolw that the .connection has .been established by the disappearance of the toriecode sgnalsfandwhjel will .then

ringuthe called party.l 1f the called party is on avmultiparty line, thecalling subscriber will ring the wantedparty nshlnguthe proper ringing code. if lthe called partys line is busy, .t he calling subscriber receives abusysignaL Athe call isfrorrr one rural area to asubscriber. vin an adracentrural area, the calling subscriber willrst llisten for the code reprlesenting'the desiredruralare'a, depress y the sy/ itczhhoolc foran instant Vto connectf to .a'trunkleading tothe desired .rural area, and then listen-for. they code allogatedto the AWanted party. .If thetrunk tothe adjacent ruralarea orthe ldesiredpartys.line is busy, the calling vs nhscfiber Awillieceive a busy sgnal. With this,excep tion, the. procedure is the same as forcalls within thesame r alilarea. If the c'allis from one rural .area to a subscriber in a rural area reached through an adjacent rural ,area `theeeilling. subscriber first listens for the code representn1g the adjac ent .rural area, depresses the switchliook for an instant, then listens for the code representing therrtore rernoterural area, depr esses the 'switchhook again for an instant, listens for the .code `of -the desired tparty, and rie-presses the switchhook yet ,again fof aninstarrt to establish vthe connectio'n'.V If either`th'e in'teroftice trunk or the wanted subscribers' line is busy, the callimg ,subscriberwill receive a busy signal; other-'Wise' the 6 procedure on the .part of the calling subscriber i's thf saine .ashasbeen described. i

l Or1 .calls .to the master olice A, the procedure is the same, as has been' described, `vvith the excepfion'that-ihe .master oiceioperator is' called in on the conectinvvith `rat-lirle--larnp.signal and .it is not necessary-foi' l-thefcalling .ruralsubscriber toringthe pe1'2 .t`c` t.V 'Iimin'g equipment is provided at each rural exchange to nite period of time.

hold connections established at that exchange for a deti- After the expiration of this time interval, the connection is automatically released at that Vrural exchange. If two or more rural exchanges are involved in a connection, two or more timing equipments may be involved, and these timers may not time exactly the same. However, a warning signal is given to the calling subscriber before any of the timers release the connection, and the calling subscriber may continue his conversation by depressing the switchhook for an instant which resets all the timers involved, so that they start anew to measure the timing periods. Suitable-arrangements are provided whereby in each rural otlice calls are established one at a time, and a multiplicity of calls are established approximately in the same order as they are originated.

The tone interrupter and control cam equipment, provided n the rural exchanges and diagrammatically illustrated in Fig. 6, will rst be described, since it is believed that this will facilitate the reading of the following description of the operation of the system in setting up calls.

Mounted upon the rotating shaft 600 is a cam disk 601 the periphery of which is cut with narrow (dot) and wide (dash) teeth representative of the codes allotted to the subscribers lines and to the outgoing trunks. As illustrated, provision is made for twenty codes which may be apportioned between substation lines and trunks, as desired. At the lower part of the figure there is indicated a linear representation of the periphery of the cam disk 601. A spring brush 602 bears on the periphery of the disk 601v and as the disk 601 and shaft 600 rotate, acts lto close the contacts 603 to apply tone intermittently from the supply 604 to the leads 605, 606, interrupted in accordance with the codes. These leads deliver the coded tones to the cross-bar switch circuit of Fig. 3. A second toothed disk 607 mounted on the shaft 600 actuates contacts 608 to apply interrupted busy tone to the leads 609, 610 as the shaft rotates which leads are multiplied to all the line circuits and interoice trunk circuits, and a third cam disk 611 is arranged to actuate contacts 612 to ground periodically the timing lead 613 for a purpose which will be explained later. A continuous tone signal is supplied over the leads 614, 615, independently of the rotation of the shaft 600 and disks 601, 607, and 611. The leads 614 and 615 are multiplied to all the line circuits.

Mounted on the shaft 600, which rotates in a counterclockwise direction, is a slip ring 616 (shown in extended form) engaged by a brush 617 connected to a lead 618 which is connected with the cross-bar switch circuit. A brush 619 is iixed to the slip ring 616 and makes contact with a stationary commutator 620 (also shown in extended form). The vertical line 621 indicates the point on the extended commutator 620 which is aligned with the make contacts 603. A commutator segment is provided on the commutator 620 for each code combination on the cam Vdisk 601, and each segment is connected to a diierent lead 6221, 6222, 6223, etc. extending to one end of the winding of a respective hold magnet of the crossbar switch (Fig. 3). The commutator segments are so positioned and are of such relative widths that a circuit is held prepared over the lead 618, brush 617, slip ring 616, brush 619, a segment of commutator 620, and a lead 622, for the appropriate hold magnet of the crossbar switch, in the interval during the transmission of each code signal over the leads 605, 606.

Rural subscriber calls another subscriber on same rural office A calling subscriber at substation 200 connected to the rural line circuit of Fig. 2, cranks his magneto 201, thereby energizing a line relay 202 bridged across the talking conductors in series with a condenser 203 in the rural line circuit. The subscriber immediately raises his receiver and listens. Upon raising his receiver, the subscribers line is closed and this completes an obvious circuit through relay 208 which operates. Relay 208 operates 209 which is slow releasing. Neither of these re- 4 lays 208 and 209 perform any function at this time. The

` operation of relay 202 closes van obvious circuit for relay 204 which is made slightly slow releasing and which locks to ground at back contacts of relay 205 and extends this ground to the lead 206 extending to the crossbar switch ing circuit, Fig. 3.

In the crossbar switching circuit, each of the leads,

such as 206, from the respective subscribers line circuits,

extends over back contacts of a common relay 300 to an individual relay 301, 302, 303, etc., and when a call has originated on a rural line, the ground connected over the lead 206 operates a relay, such as 301, associated with the particular calling rural line. If several calls are originated simultaneously, the relays 301, 302, 303, etc., of'those lines will operate and lock up to the ground on their respective leads 206.

As previously stated, the operating paths for the relays 301, 302, 303, etc., extend over back contacts of the common relay 300 which energizes over an obvious circuit as soon as any relay 301, 302, 303, etc. operates. This prevents any other of the relays 301, 302, 303, etc., from operating until calls already admitted within the gate" have been handled and all the energized relays 301, 302, 303, etc., have been released. At that time another group of waiting calls will be admitted within the Y gate for attention. This arrangement is provided to enable the calls to be handled approximately in the same order as they were originated. It will be noted that the uppermost contacts of the relays 301, 302, 303, etc., are connected in a chain circuit to permit the calls awaiting attention to be handled one at a time and in a regular order from left to right of the relays 301, 302, 303, etc. The ground for assigning the line and for the further operation of the switching circuit is provided from the bottom make contact of relay 300. Atcontacts of the first operated relay 301, 302, 303, etc. this ground from relay 300 is connected to and energizes the particular one of the horizontal or select magnets 304 of the crossbar switch 305 and also one of the relays 306 particular to the calling line receiving attention.

The rural substation lines and the interoice trunks are connected to both the horizontal and vertical terminals 307, 308, of the crossbar switch 305, the horizontal terminals 307 being used on calls originated on the rural.

lines or trunks, and the vertical terminals 308 being used on calls completed to the rural lines or trunks. These connections are shown in heavy lines.

The operation of the individual relay 306 causes the tone code signals which are received from the tone interrupter of Fig. 6 over leads 605, 606 to be connected over leads 309 and 310 and back contacts of the relay 207, Fig. 2, to the calling subscribers line.

When the calling subscriber recognizes the code signal particular to the wanted local rural subscriber, he signals by vibrating his switchhook. The down movement of the switchhook opens the direct current path through the subscribers loop, and relay 208 releases. Since relay 209 is slow to release, ground is momentarily connected over break contact of relay 208 and make contact of relay 209 to the lead 210, and a circuit is completed over lower make-contacts of the particular relay 306, Fig. 3, and lead 618 to the tone interrupter and control equipment of Fig. 6. If the calling subscriber has'vibrated orv depressed his switchhook on the proper tone code signal, this ground will be switched through the brush 617, slip ring 616, brush 619 and the commutator 620 to the proper lead, for example, lead 6222 extending to the proper vertical or hold magnet 311 of the crossbar switch 30S which operates and establishes the desired connection through the crossbar switch 305. When this is done, ground is applied over the lead 312 to energize the relay 205, Fig. 2, which opens the locking circuit of relay 204, thereby removing ground from the lead 206. This removal of ground from the lead 206 allows the associated relay 301, Fig. 3, to release, and the crossbar switching .circuitto advance tothe next waitingcall. :Inwill'bemoted .that the release of relay i301 also -releasesihe associated relay v306 and thecrossbarstvitch select .magnet i304. :'It will also be -noted-thattheground on thelead =312fis.ex tended over back contacts of relay 1223, :lead 225, and .horizontal and vertical terminalsof.thepperated crossbar switch 305 to the sleeve lead 225' .of ithe.called=line. The lhold magnets 311 are provided .withmakefbeforebreak contacts over which they'lock up--tofthegrounded .sleeve leads.

T-hecalling subscriber will knowithat the ,connection .has been established by the disappearance of the ,tone code -signals which are disconnected .at :frontcontacts of relay 306, -and he will :then ,ring -the called 4.party by cranking his magneto 201. Since .the-relay 205 is-,now energized, the 4further operationoffrelay 202-will close a .circuit for relay i211 vwhich at.its.malce contact applies ringing current to the callediline. aIfAhe called party -is on amulti-party line, -the calling.subscriberwillring thenecessary code. Relay'208,.which remainscnergized when the switch-hookzat the snbfstatiouzis-in its .raised position, also closes a circuit -forrelay 1212 :which at its make -contacts connects talking :battery :to .the ,cailed subscribersA line. It will be observedthat -the.relay, such as 213, in the called subscribers =line circuit.will1=haue been operated over the grounded sleeve flead, suchas 225' which leads to that line, andthatithesnormalfhattery supply of the called line will havezbcen --disconnected AThe operation of any individual-relay 306,;1'1`ig. 3., which connects up thetone code signalsalso aconnects a ground to the lead '3l-3 to energize a commonrelay 314 to start a timing circuit 315. `Relay .314 connects wbatteriy over an interrupter 316 and resistance i317, .-.tO-Ghargeia condenser 31'8 to a sufficient voltage to Ifire zafcoldlcathode tube 319 and operate .a relay v'320. The desiredftirne intervall is obtained .by adjusting-thefyaluesfof the resistn -ance 317 and condenser r318. Should the called'linefbe -the ground on the lead -206 thereby dci-energizing the relay 301 of the switching circuit, Fig. 3, and causing such swtiching circuit to advance tothe next .waiting call.

Assuming that the calledline is free, -two timing-circuits 215, 216 in the line circuit, Fig. 2,-come intov operation upon -energizationof relay 205. -These `timing Acir- -cuits are .similar to the timing circuit-315 of=Fig. 3, but 1 -further lengthening of the timeintervalis obtained by vthe introduction of a common relay 5217,.which5-is opv-.erated from ground through contact-612, closed by an interrupter cam 611, Fig. 6, over the lead 613. -Atrnalte contact of this relay connects battery to an amature of all the relays 205 associated with the line circuits. The ':irst timing circuit 215, comprisingcondenser-218, cold -cathodetube 219 and relay 220, is arranged after,say,

four minutes, to connect a steady tone from -thevleads 614, i615, Fig.- 6, to the calling subscriber-s 1i ne, indicat- --ing :that the allotted conversation time-has-alrnostexvpired andthat the-calling subscriber must give-a ringing signal iffhes desires to continue his conversation.

The second-timing circuit 216, comprising condenser 221, cold cathode tube-222 and relay 223, isset for a .slightly longer in tervaL; say, four and one-half minutes, :jeudis-arranged to force the release Vof the .connection .3bya'liscQnnectingaground if the subscriber does not indi .tacts .removes .the .ground .on lead 31:2 from fthe sleeve :leads 225,fg225', .thereby v.unlocking thejhold magnet 3131. V'This `results in the release of :the Arelay I:205 .and .fthe retur-nofthe .ruralzline circuitrto its nOlmalcondition. A ringing signal=fromftl1ecalling subscriber-:indicating that he .desires tocontinue would again energize relay20 2, which willdischarge the condensers 21g-8 and 221 .and defionize -the cold.cathodetubes 219 .and 222causing both `timing -circuits to start anew before the relay 223 operates.

vthe distant. rural cnice.

:Calls :from.a.subscriber. .of one rural .oice ,.-to asub- .scriberof a distant rural .ocemake .use,at.each .rural of- .ce of a ruraliinteroce trunk ycircuit which is shown vin Fig. 4. 'The-leadsatthe right hand side vof this circuit in a ruraloiiice Acorrespond -to thezleadsat theright-.hand side of the line circuitof Fig. 2 and connect to a set lof leadsin the crossbar-circuit of Fig.- 3 corresponding. to

vthose ou-the left of Fig. f3 but .which are -individualfto -the trunk circuit,.except -that leads .61-3, 61.4 and 615 .of

-Fig.,.3 have .no-counterpart in lFig. 4, since they are lnot AThe outgoingend (conductors 419, 420, 422) ofithe ruralinter-oice Itrunk circuit, shown in Fig. 4, is con- .nected to a particular setofthe vertical terminals of the 4crossbar switch, whilst the incoming end (conductors 412, .413, 414, .418.) is connected to a particularsetof thehorizonta'l terminals. The talking-conductors 407 and 408 lead to thev distant office and are connected to similar vconductorsoi the interoice trunk circuit .at that ofce.

.-If the call is 'fromonerural cnice, for instance, -that shown in Figs. A2 and 3, to asubscriber in a distantrural ndice, thecalling subscriber cranks-his magneto, as in -the Acase .of :a local .call, land .will listen .for :the vcode representing -the .outgoing trunk leadingto the desired distantrural exchange. Hewill then Vmomentarily-de- ``press .his switch-hook, las in :the .case Aof a .local call, and in.thefcrossbarswiteh of hisruraloicea hold magnet,.such as 311-of the vcrossbar .switch 3.05 of Fig.

will be operated and establish a connection over the talking-conductors 419 and 420 .of-the trunkcrcuit (L-Fig. v4) at that-oticeand the.talking.conductors 407 and .408 to the rural interoiice trunk circuit, Fig. 4, located -at Relay .421 of .the trunk circuit at the calling exchange is energized over the sleeve ywire 422 and talking battery lis fed over the trunk leads 407 and.408 from the callingline circuit. Relay 400 infthe trunk .circuit-atthe distant .oce operates from .battery and ground at Afront contacts -of lrelay -212 Ain the .call' ing line circuit, and slow releasetrelay .401 is ,energized over an -obvious circuit,therebymaintaining.ground on lead 402 over back contacts of relays 4.03 and 404. `rll`he ground on lead `402 causesthe-.crossbarswitching. circuit in the .distantrural V,office to Ifunction, .as .already v.described in connection with Fig. 3, whenground was connectedto-lead 206 from-.the subscribers line circuit lof Fig. 2. The .crossbar switching vcircuit vat the distant rural exchange will -return-a second set .of tone .code signals to the callingfsubscriber over conductors 405, 4.06, corresponding to .309, .310, back contacts of relay 403 and the talking conductors i407, .408 of the interoftice -tr-unk circuit to thetrunk circuitof the calling. ndice-and over talking .conductors 419 and 420 and-thecrossbar switch of Fig. 3 to the calling'line. When-the calling `subscriber hears the lproper to'ne. codesignal, vdesignating -Qficegand establishthe desltsd ing line circuit. The ringing current will pass overy the talking leads, through the crossbar switch at the calling exchange, through the transformer of the trunk circuit of the calling exchange, and will enter the trunk circuit of the distant exchange over the talkingleads 407 and 408. Relay 410 will operate and will operate relay 411. Relay 411 will apply ringing current to the called line over the trunk conductors 412, 413, which are now connected to the called line over the crossbar switch in the distant rural oice. The operation of relay 404 removes the ground on the lead 402 and the switching circuit at the distant rural otlce is allowed to advance to the next wating call. Should the called line be busy and the switching circuit be unable to complete the desired connection within the established period of time, or should the calling subscriber fail to give the switch-hook signal within the predetermined time interval, as has been described in connection with a local call, a ground will be received over the lead 415 from the timing device of the distant rural office, corresponding to the device 315 of Fig. 3, to energize the relay 403, which locks to the grounded lead 414. The operation of relay 403 causes a busy tone signal on the leads 416, 417 from the tone interruptcr equipment of the distant rural ollice (corresponding to leads 610, 609, Fig. 6), to be transmitted over the talking conductors 407, 408 to the calling subscriber. The operation of relay 403 also opens the ground on the lead 402 (extending to a lead of the switching circuit of the distant rural office, corresponding to lead 206 of Fig. 3) and allows the switching circuit at the adjacent rural otlice to advance to the next waiting call.

When the calling subscribers line circuit times out and the rural interotlice trunk is released at the rural exchange to which the calling subscriber belongs, relays 400 and 401 will be de-energized. By the release of these relays, a circuit is closed for slow operating release relay 423 which disconnects ground from the lead 418 causing the switching circuit atthe distant rural ollice to be released. Ground is thereby removed from lead 414, relay 404 is de-energized, and the trunk circuit restored to its normal condition.

If the call is from one rural oliice to a subscriber in another rural oiiice reached through an adjacent rural ofiice, the calling subscriber first listens for the code representing .the adjacent rural oice, momentarily iepresses his switchhook, listens for the code representing the more remote local office, again momentarily depresses his switchhook, listens for the code of the desired party in the more remote rural office and again momentarily depresses his switchhook to complete the connection. If either of the interotce trunks or the wanted subscribers line are busy, the calling subscriber will receive a' busy signal. All these operations take place as already described and will be readily understandable to those versed in the art.

As a means for subscribers to detect the advancement of the connection from one ollice to another, a dilerent tone pitch may be used for the tone code signals in adjacent exchanges.

Master office trunk circuit The master oliice trunk circuit, illustrated in Fig. 5, is arranged for incoming and outgoing tralic and the procedure in setting up a connection on an incoming call is the same as has been described in connection with a call to an adjacent rural oflice, since the trunk terminates at the distant rural oiiice in a trunk circuit, as shown in Fig. 4. When the trunk circuit is seized at a distant rural ofce, the relay 500 is energized over the talking conductors 501, 502. The energization of relay 500 lights the answering lamps 503, and when the operator plugs into an answering jack 504, relay 50S energizes over the sleeve and extinguishes the lamp signal. The operator ascertains the calling parties requirements and completes the connection in any well-known manner.

On an outgoing call to the rural oiiice, the operator will plug into a multiple jack 506 of the trunk circuit, thereby energizing relay 507 over the sleeve. Relay 508 does not operate at this time, because the operators circuit is arranged to be open for direct current. The operation of relay 507 disconnects relay 500 from the talking conductors and connects battery and ground thereto to energize a relay, such as 400, Fig. 4, in the rural oice, to start the switching circuit at the rural oice to function and return the tone code signals, as already de scribed in connection with an interoice call. When the operator hears the desired signal, she will intermittently -operate the relay 508 by completing the direct current connection and in turn the relay S09 to cause the distant switching equipment to establish the connection, as already described. When the operator actuates her ringing key, relays 510, 511, operate, the last-mentioned relay connecting ringing current over the trunk conductors 501, 502 thereby operating ringing relays such as 410, 411, Fig. 4, in the trunk circuit at the distant end of the trunk. No disconnect signal is given to the operator at the end of conversation and it is necessary for her to monitor in on the connection to know when the trunk should be released.

While I have described and illustrated one speciiic application of my invention, it will be clear to thosek versed inthe art that variations in the manner of carrying out my invention may be made, as well as re-arrangement of the circuits, without departing from the spirit and scope of myinvention as defined in the appended claims. For example, instead of tone code signals, a magnetic or other voice recorder may be provided at the central oflice or position, so that a calling station party hears a roll call of the other subscribers or other offices by name as the connections are prepared by the switching equipment. Moreover, it will be understood that the term station lines used in the claims embraces both subscriber-station lines and trunk lines to other oliices.

What I desire to claim and secure by Letters Patent is:

l. A telephone system comprising a plurality of` station lines, central ofce switching equipment, connections from said station lines to said switching equipment, means at said central office responsive to an operation at a calling stationfor cyclically preparing said switching equipment successively to make connection to said station lines, means at said central ofiice for successively and in synchronism with said preparing means transmitting discrete distinctive signals to said calling station, each discrete signal being characteristic of the identity of a diierent station line to which connections are prepared, and means at said central oflice responsive to a further operation at said calling station for actuating said switching equipment to complete a prepared connection to a wanted station line.

2. A telephone system, according to claim l, further comprising a timing device at said central oice associated with a station line circuit and means controlled by said timing device for forcing release of an established connection after a predetermined time interval.

3. A telephone system comprising a plurality of station lines equipped with rnagnetos, a central oflice, switching equipment-at said central oflice, connections from said station lines to said switching equipment, an interrupter and control device at said central ofce, relay means-at s, 'monat said central oiiice responsive to the operation of 'a magneto at a calling station for causing said interrupter and control device to prepare cyccally said switching equip ment to make connection successively to said station lines and to apply synchronously with the cyclical preparation of said switching equipment to said calling station line distinctive signal currents characteristic of the identity of the station lines to which connections are prepared, and relay means at said central oflice responsive to a signal from said calling station for actuating said switching equipment to complete a prepared connection to a Wanted station line.

4. A telephone system, according to claim 3, further comprising timing means at said central oice associated with a station line circuit for applying a distinctive tone signal to said calling station line from said interruptor and control device a predetermined time interval after the initiation of the operation of said timing means, means responsive to establishment of the connection to the wanted station line for initiating the operation of said timing means, means for forcing the release of the connection after the lapse of a further predetermined interval, a circuit for resetting said timing means, and means controlled by said first-mentioned relay means, responsive to the further operation of said magneto prior to the lapse of said further interval, for closing said circuit for resetting said timing means.

5. A telephone system, according to claim 3, further comprising a relay chain circuit at the central oice for permitting waiting calls on station lines to be handled one at atime, and timing means for causing said relay chain circuit to advance to a next Waiting call if a calling station line does not complete a prepared connection to a wanted station line within a predetermined time interval.

6. A telephone system, according to claim 3, further comprising a relay chain circuit at the central oiiice for permitting waiting calls on station lines to be handled one at a time, and means for causing said relay chain to advance to a next Waiting call responsive to the completion of a prepared connection.

7.A telephone system, according to claim 3, further comprising a iirst and second relay at the central oiiice individual to each station line, a third relay, a circuit for energizing the appropriate rst relay over contacts of said third relay responsive to a station line being placed in a calling condition, a chain circuit including contacts of said first relays and including contacts of said third relay for energizing the appropriate second relay, parallel energizing circuits for said third relay over contacts of said rst relays, and contacts on said second relays over which said distinctive signal currents are applied to the calling substation line.

S. A telephone system comprising a plurality of station lines, a central oiiice, a cross-bar switch at said central oice having sets of horizontal and vertical terminals and horizontal and vertical magnets for actuating said sets of horizontal and vertical terminals respectively, connections from each said station line to a set of both horizontal and vertical terminals, means for transmitting a calling signal from a calling station to said central oiiice, means responsive kto said calling signal for operating a horizontal magnet particular to the calling station and for cyclically preparing circuits for said vertical magnets, means at said central oiiice for successively transmitting signals to said calling station. `:ach signal indicating thereat the condition of said cross-bar switch, means for transmitting a further signal from said calling station to said central oiiice and means at said central oiiice responsive to said further signal for closing a circuit for a vertical magnet for completing a connection to a wanted station line.

9. A telephone system comprising a plurality of station lines, a central oiilce, switching equipment at said central oiiice to which said lines are connected, a commutator device at said central oice, signal means at a calling station for transmitting a calling signal to said central oii'ice, means at said central oiiice responsive to said calling signal for causing said commutator device cyclically to prepare said switching equipment to make connection to said station lines in turn, an interrupter disk synchronously rotated with said commutator device and provided with cams characteristic of codes allotted to the respective station lines, ,interrupter contact springs adapted to be actuated by said disk, a source of tone current, means for applying said tone current to said calling station line over a circuit including said interrupter contact springs, means at said calling station for transmitting a connecting signal to said central ofiice, and means at said central otiice responsive to said connecting signal for actuating said switching mechanism to complete a connection to a station line, as indicated by a characteristic code tone signal applied to the calling station line.

l0. A telephone system comprising a plurality of station lines, a central oiiice, a cross-bar switch at said central office having sets of horizontal and vertical terminals and horizontal and vertical magnets for actuating said sets of horizontal and vertical terminals respectively, connections from each said station line to a set of both horizontal and vertical terminals, a commutator device at said central oiiice, signal means at a calling station for transmitting a calling signal to said central office, means responsive to said calling signal for causing said commutator device cyclically to prepare circuits for said vertical magnets in turn, an interrupter disk synchronousl; rotated with said commutator device and provided with cams characteristic of codes allotted to the respective station lines, interrupter contact springs adapted to be actuated by said disk, a source of tone current, a circuit including said interrupter contact springs connected to said station line, means for applying said tone current to said calling station line over said circuit, means at said calling station for transmitting a connecting signal to said central oflice, an energizing circuit for each of said vertical magnets, and means at said central oiiice responsive to said connecting signal for completing the energizing circuit for the respective vertical magnet the circuit of which is prepared at the time said connecting signal is transmitted.

Taylor et al. May 27, 1947 Baker Feb, 6, 1951 

